The present invention relates to loudspeaker enclosures of the low frequency exponential folded horn type primarily intended for corner placement, however is capable of free-standing use as needed. In particular, the present invention features a relatively large-area unitary throat pathway which is bifurcated horizontally at the rear of the enclosure, and exhausts in a relatively forward direction.
The Klipsch and Delgado AES paper, “A Revised Low-Frequency Horn of Small Dimensions”, Vol. 48, No. 10, October 2000, describes a dual 12-inch driver folded horn enclosure featuring throat bifurcation of the horn channels which are horizontally folded. A defining feature of the device is the forward-canted terminal channels exiting on each side of a central planar baffle. The use of forward-canted exit splay angles is explained as providing an increase in upper band pass frequency response by more direct wave propagation to the audience. Due to the throat bifurcation, the access opening to the drivers is required to be on both the top and bottom of the enclosure. The device is configured specifically for a particular driver with explicit parameters.
Another prior art example is my previous U.S. Patent Application Pub. No. 2005/0276431 titled “Top-Loading Folded Corner Horn” which also features a bifurcated-throat horn pathway which folds exclusively in the horizontal plane, however, it does not incorporate forward-canted exit channels, instead, it exits along the side walls of the corner. The indirect exit channel splay-angles do provide a physical limitation to the upper frequency limit in which it can propagate without apparent distortion. In order to achieve an even higher crossover point as compared to my previous invention where the limit appears to be 600 Hz, the use of forward-angled exit channels to allow a more direct path to the listening position is seemingly required. The inclusion of forward-canted exit channels bears with it the added complication and weight of including external side walls to fully enclose the horn pathway. Several factors also enter into the contemplating the benefits of such an addition would make to the single 15-inch driver device. For instance, the built-in outer side walls would free the enclosure from requiring external planar boundaries to be in close proximity. This allows for a more generalized placement for the enclosure, while still allowing for ⅛th space placement for achieving the maximum low frequency response, however, it also would greatly increase the overall weight and the-complexity of construction, for relatively little increase in utility.
The increased capabilities presented by the use of dual drivers also provides useful benefits, such as providing wiring options which effect efficiency and power handling capabilities, overall sound pressure levels, and a naturally shorter horn path length for a given low frequency cutoff (Fc) due to a larger effective throat size. It is well known in the art that horn pathway lengths below a certain division of wavelength will suffer from variances in reactance and subsequently produce peaks in the response unless the reactance is properly annulled. The horn path length is dependent on the mouth size, throat size and the chosen flare rate. The U.S. Pat. No. 4,210,233 to Gillum et al., teaches the minimum mouth size [area] for corner placement can be as small as 1/12 wavelength [in diameter] if the driver is properly annulled. It can be assumed that the horn path length is also, as a matter of course, shortened if the throat size and flare rate remains unchanged. Conversely, horns with large throat areas, proper mouth sizes, and having short pathway lengths require reactance annulling due to the short pathway lengths involved in order to maintain a relatively flat response over the operating band pass.
A particular drawback of using dual 15-inch diameter drivers is that the overall footprint of the device must be increased to accommodate a relatively large (78 square inch) throat area per driver especially if bifurcated at the throat. The use of smaller throat cross-section channels would tend to limit the maximum sound pressure level due to air overload distortion, and possibly require the use of smaller diameter drivers to compensate. This problem is typically overcome by employing a rapid flare rate at the throat to modify the effects of excessive reactance that a more confined flare rate (of lower Fc) of a relatively small channel cross-section would embody.
The ability to achieve lower distortion, in a general sense, is that large throat cross-sections can allow for higher air velocity transit compared to a more restricted channel, and therefore throat overload distortion limits are relegated to the more extreme end of the performance curve.
Another consideration that particularly effects front-loaded horns in general is thermal voice coil overload or failure in sustained high sound pressure level (SPL) use. This aspect is compounded in the case of dual-drivers in a sealed back chamber, and may be exacerbated by the tendency of modern high wattage drivers requiring smaller back chamber air volumes than in the past for reactance annulling purposes. It seems advisable that, in the case of high wattage drivers in a infinite baffle configuration and used for prolonged periods at a high sound pressure level (SPL), should be provided an adequate means of cooling the voice coils, such as conducting the generated heat to a heat-sink assembly located preferably outside the back chamber. This object, while technically achievable in the case of a bifurcated-throat design such as the previously cited prior art designs, may not be economically practical due to the complications imposed by the position of the driver(s).
Considerations of footprint size are probably most important in domestic use, however, overall footprint size can also be seen to be inextricably related to enclosure weight, a definite factor in public address use where portability is perhaps the major concern. Enclosures with the best balance of size, weight and performance capability would seem to be the most desirable, regardless of the application. In public-address (PA) including live music applications where higher SPL's are generally desirable, the use of additional bracing for preventing internal enclosure wall vibration adds weight to the enclosure, and effects portability. The tradeoff for domestic situations seems to be that low frequencies with relatively high efficiencies typically means a larger enclosure, with the attendant larger footprint, and the tradeoff for PA use is that achieving high SPL's typically means heavier (or multiple) enclosures are required.
For PA applications, it is reasonable to assume that multiple smaller-volume cabinets (for stacking) allow for easier porting and packing for transportation purposes than a comparable single, larger-volume cabinet would. However, it seems reasonable for domestic situations, where semi-permanent placement is assumed, and perhaps appearance is an important consideration, that a single large-volume cabinet would be more desirable.
Home Theater (HT) market considerations conceivably fall somewhere in between the typical domestic use, such as a living room, and a PA application. It is typically a much smaller venue than a PA application, but shares some of the same issues, such as overall clarity, maximum SPL, and the presentation of the human voice. The HT market may include less concern for appearance than would the typical domestic situation, for instance, black finishes seem to be preferred as movies tend to be viewed in darkened spaces. Overall footprint size may also be less of a concern when a dedicated HT space is involved. The dynamic soundtracks typical of digital media may require prolonged periods of intense SPL's than common in domestic use, such as listening to high-fidelity (HI-FI) music exclusively. In particular, it can be assumed that the requirements of reproducing highly dynamic sound effects impose somewhat different demands on loudspeaker systems than does music alone.
A loudspeaker enclosure capable of reproducing the low frequency dynamic range available with current digital technology, at relatively high sound pressure levels, if needed, with low distortion, employing a relatively small footprint, and which allows for public address, home theatre, use as musical instrument speakers, and domestic high fidelity use would be highly desirable.